I agree that many people, not just teenagers, will experience hearing loss due to mp3 players. What I find amazing is the narrow-mindedness of an "audiophile" describing certain types of music as "crap". I'm sure there are many members here that listen to such crap!
BTW, I do listen to Jazz on my iPod. 
Sorry if looks old-fashioned or outdated of my part. Iam reffering to the kind of music in MTV channel, where many bands sound all the same, and as made in a serial line by an hurry unlettered musician.
The songs elements are always the same, as heavy distortion guitar, singer with a squeaky voice and screaming, a unremitting drums and cimbals, and irrelevant aggressive or emo lyrics, not to mention the womens Pop singers.
Seems to me all teenagers bands are Hardcore or Pop. Iam aware MTV and Radio stations charge money or advertisiment to play these songs.
I wonder how bad will be the teenagers music in 10 years/.
Regards